1. Field of the Invention
The present invention generally relates to asynchronous mobile telecommunication terminals. More particularly the present invention relates to a method and apparatus for managing demodulation timings on a cell-by-cell basis.
2. Description of the Related Art
Third-generation (3G) mobile telecommunication systems use code division multiple access (CDMA) technology, and provide a consistent set of services capable of transmitting packet-based text, digitized voice or video, and multimedia data at data rates of 2 megabits per second (Mbps) or more no matter where mobile phone or terminal users are located in the world. These 3G mobile telecommunication systems are classified into universal mobile telecommunication service (UMTS) adopted as the European standard and CDMA-2000 adopted as the American standard.
CDMA-2000 is a synchronous mobile telecommunication system based on second-generation (2G) CDMA systems such as Interim Standard-95 (IS-95), J-STD008, and so on used in South Korea, the United States, Japan, and others. UMTS is an asynchronous mobile telecommunication system using CDMA on the basis of a global system for mobile communications (GSM) and general packet radio services (GPRS) widely used in Europe and other regions.
Conventionally, a synchronous cellular mobile telecommunication system is synchronized with global positioning system (GPS) clock on a cell-by-cell basis or on a Node B-by-Node B basis in a wireless environment and transmits data at designated times. Accordingly, once synchronization is acquired through a pilot channel, the system does not need to acquire synchronization for other cells and demodulates data by using existing timing information.
On the other hand, an asynchronous cellular mobile telecommunication system transmits data at different times on the Node B-by-Node B basis (hereinafter, referred to as the cell-by-cell basis) regardless of GPS time. Then, an asynchronous user equipment (UE) acquires transmission timing for each cell which uses a common pilot channel (CPICH) serving as a reference signal sent on the cell-by-cell basis, and demodulates data in synchronization with the transmission timing.
In the asynchronous UE, fingers demodulate multipath signals of a radio channel and transmission timings are managed on a finger-by-finger basis. The fingers are hardware devices for demodulating the multipath signals in a RAKE receiver. Control information for controlling the operation of each finger is managed in a register file such that the fingers can refer to the control information. The register file includes information and commands for controlling hardware of a physical layer using a control message of a higher layer in a microprocessor.
FIG. 1 is a table illustrating a conventional register file having control information for finger-by-finger management.
Referring to FIG. 1, RefFinger 102 is information for establishing a reference finger among a plurality of fingers provided in the UE of an asynchronous system. F#CodeID 104 is information for establishing scrambling codes on a finger-by-finger basis and finding cell-by-cell timings of data sent from Node Bs to a UE. F#ChOffset 106 is information for establishing CPICH offsets on a finger-by-finger basis to transmit information to the fingers. F#Mode 108 is information for establishing diversity modes on a finger-by-finger basis. The diversity modes are space-time transmit diversity (STTD) mode, transmit adaptive array (TXAA) mode, normal mode, and so on.
A physical layer of the asynchronous UE is configured such that it can receive control messages downloaded from a higher layer configured by a microprocessor on a finger-by-finger basis. Accordingly, the asynchronous UE receives control information for scrambling codes, channel offsets, diversity modes, and so on from a higher level on the cell-by-cell basis, manages the control information in a register file, and distributes the control information on a finger-by-finger basis.
As described above, the conventional UE of the asynchronous mobile telecommunication system repeats an operation for reading control information sent on the cell-by-cell basis and distributing the read control information on a finger-by-finger basis a number of times corresponding to the number of fingers. Accordingly, there is a problem in that the occupancy time and load of the microprocessor increases. When the asynchronous UE manages data sent from cells at different times on a finger-by-finger basis, communication may be dropped when a soft handover is performed.